Can MEMS-based particulate matter sensors reliably measure mass?
Résumé
Micro-electro-mechanical systems (MEMS) have emerged as promising candidates for particulate matter (PM) mass sensing due to their high sensitivity and integration potential. However, their practical deployment is hindered by unresolved challenges in calibration and sensor behavior interpretation under different loading conditions. In this work, we present a combined theoretical and experimental framework to investigate the performance and limitations of MEMS-based PM sensors. A bulk-mode MEMS microbalance with T-shaped tethers was designed to simultaneously address key issues such as active surface area, spatial sensitivity, and parasitic feedthrough currents. Controlled polystyrene latex (PSL) particle deposition experiments were conducted using an inertial impactor, and deposited masses in the nanogram range were estimated through automated microscope counting. Frequency shifts were measured using a lock-in amplifier and analyzed for different spherical particle diameters ranging from 1 µm to 7 µm. The results reveal significant deviations from the classical mass-loading relationship and are explained through a modified Sauerbrey model that incorporates particle-substrate contact mechanics and rolling dynamics, leading to an effective mass term dependent on particle size and adhesion. Smaller particles were found to appear “heavier” than their physical mass, while larger particles were found to appear “lighter”. This study demonstrates that MEMS-based PM sensors are not purely mass sensors, but rather multi-parameter systems influenced by particle adhesion and inertia. These findings highlight the need for a re-evaluation of existing calibration strategies and open new perspectives for designing MEMS sensors capable of extracting both mass and contact-specific information from airborne particles.
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